The city of San Francisco can't make retailers display signs and stickers with information about cellphone health risks, but it can require retailers to give customers an information sheet about it, a federal judge ruled on Thursday.

The CTIA, an organization representing mobile phone operators, brought a lawsuit after the city passed an ordinance requiring retailers to hang posters noting that cellphones emit radio frequency energy. The posters also would offer tips for avoiding health risks possibly associated with such RF energy. In addition to the posters, the ordinance required retailers to place stickers with the warning on store displays and provide customers with fact sheets about limiting exposure to RF.

Judge William Alsup, who is presiding over the case in the U.S. District Court for the Northern District of California, found that requiring retailers to hang the poster "is not reasonably necessary and would unduly intrude on the retailers' wall space."

He also said that the sticker requirement is unconstitutional because it will "unduly intrude upon the retailers' own message."

He did, however, allow the requirement that retailers give each customer a fact sheet developed by the city, as long as the city accepts a few of his edits. While each of the facts on the sheet is accurate, the overall message is misleading, he wrote. "The overall impression left is that cell phones are dangerous and that they have somehow escaped the regulatory process. That impression is untrue," he wrote.

The ordinance says that retailers must give the fact sheet to everyone who buys a phone and to any other shoppers who request the fact sheet. Retailers will be fined for failing to comply.

To make clear that the U.S. Federal Communications Commission already regulates cellphones, Alsup asked that the city add this line to the fact sheet: "Although all cell phones sold in the United States must comply with RF safety limits set by the FCC, no safety study has ever ruled out the possibility of human harm from RF exposure."

"If this corrective item is unacceptable to San Francisco, then the entire program will be enjoined and San Francisco should broadcast its message at its own expense rather than compelling retailers to disseminate misleading statements," Alsup wrote.

He also wants the city to explain the significance of a warning it cites from the World Health Organization. The fact sheet should include a sentence noting that the WHO designates RF as a "possible" rather than a "known" or "probable" carcinogen.

The city must also remove images on the fact sheet that show a silhouette of a person carrying a cellphone surrounded by concentric circles. The judge thinks the image could be interpreted as indicating that cellphones are dangerous, and because he doesn't see proof that they are, he is requiring the image to be removed.

The city plans to appeal part of the order. "I disagree with his decision to limit the City's message in the way he has done. We will ask the Ninth Circuit to uphold the portion of the ruling that allows the fact sheet to go forward, but we will also ask the Court to make clear that we have even broader authority to protect the health of our people," City Attorney Dennis Herrera said.

The CTIA did not reply to a request for comment made after its regular business hours.

Attorneys involved in the case are asked to meet on Nov. 4 to agree on the revised fact sheet and submit a version that conforms to the order, or competing versions if the two sides can't agree. If the city doesn't accept the judge's terms, then the entire ordinance will be overturned, he said. The ordinance is stayed temporarily until Nov. 30 to allow for appeals of the order.